In recent years, it has become fairly common to find one or more cameras deployed on a vehicle and utilized in any one of a number of applications. For example, a camera may be mounted proximate the rear of a vehicle and coupled to a display that generates images of the vehicle's rearward path to which a driver may refer when backing-up to avoid collision with a rear obstacle. Cameras have also recently been employed in lane monitoring systems that determine if a vehicle is drifting (e.g., straying or departing) from the lane in which it is traveling. When it is determined that a vehicle has drifted from its desired lane position (e.g., from the center of the lane) by a predetermined amount, the lane monitoring system may: (1) alert the driver of this condition (commonly referred to as a lane departure warning function), and/or (2) actively direct the vehicle back toward the center of the lane (commonly referred to as a vehicle heading correction or lane keeping assist function).
Lane monitoring systems configured to provide a lane departure warning (LDW) function generally employ a frontward-looking (or downward-looking) camera, a processor, and an alert generator. The processor receives lane image data from the frontward-looking camera to determine the location of lane markers, and thus the lateral boundaries of the lane, relative the vehicle. If it is determined that the vehicle is drifting too far from the center of its lane (or if the distance between the vehicle and the lane markers has exceeded a minimum threshold value), the lane monitoring system causes an alert to be generated (e.g., an audible or visual alert), which may vary in relation to the degree of drift. This alert may include a haptic alert (e.g., a seat vibration) designed to prompt the driver into performing an appropriate lane correction. One known lane monitoring system, for example, utilizes an actuator coupled to the vehicle's steering wheel to provide a driver with the tactile impression that his or her vehicle is traveling along an elongated groove with sloping sidewalls running within the lane.
Lane monitoring systems configured to provide a lane keeping assist (LKA) function (i.e., configured to perform vehicle heading corrections when lane drifting becomes too severe to actively direct a vehicle back toward the center of its lane) typically comprise a frontward-looking (or downward-looking) camera, an actuator coupled to the vehicle's steering wheel, a plurality of sensors (e.g., steering wheel angle sensor, vehicle speed sensor, etc.), and a processor that determines a target steering wheel angle from lane image data provided by the camera and from other data provided by the plurality of sensors (e.g., vehicle speed, lateral acceleration, road curvature, yaw angle, etc.). If the actual steering wheel angle differs from the target steering wheel angle by a threshold amount, the processor commands the actuator coupled to the steering wheel to apply an appropriate amount of torque to correct the discrepancy (i.e., perform a vehicle heading correction) and thus direct the vehicle back toward the desired lane position.
Existing lane monitoring systems employing one or more frontward-looking (or down-ward looking) cameras may be unable to effectively operate under poor visibility conditions (e.g., rain, snow, fog, etc.). Perhaps even more problematically, the cameras employed by existing lane monitoring systems may be temporarily blinded by direct sunlight exposure. Thus, existing systems may not perform properly when the vehicle is being driven in the general direction of the sun and there exists a low sun angle (e.g., the sun is relatively close to the horizon as during sunrise or sunset). Systems employing forward-looking stereo-camera assemblies or multiple downward-looking cameras are relatively complex and expensive to employ.
Considering the above, it should be appreciated that it would be desirable to provide a lane monitoring system having lane departure warning and/or lane keeping assist functions that is capable of operating more effectively under normal driving conditions in general and under poor visibility/direct sunlight conditions in particular. It should further be appreciated that it would be desirable that the implementation costs associated with such systems be minimized by, for example, utilizing components (e.g., rearward-looking cameras) currently deployed on a vehicle. Furthermore, other desirable features and functions of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.